1. Field of the Invention
This invention relates to photographic equipment, and more particularly to a rotary shutter mechanism for use in still cameras.
2. Description of the Prior Art
The recent development of motor drive means has enabled continuous shooting to take place at a rate of three to five frames per second; however, it is now desired further to increase the rate of continuous shooting.
Conventional still cameras adapted for use with motor drive means have employed a shutter known as a focalplane shutter which comprises two shutter curtains reciprocally movable during exposure and during winding. The shutter curtains and the actuating system therefor contribute substantial inertial mass which in turn has led to a reduction in the ability of the mechanism to accelerate rapidly, thus providing a barrier to efforts to increase the speed of continuous shooting. To avoid these problems, the present invention incorporates the rotary shutter which has usually been used in cinecameras.
Generally, the following three types of rotary shutter systems have heretofore been proposed for use in still cameras.
A first type is the system disclosed in Japanese Patent Publication No. 22077/1964, of which the embodiment of FIG. 2 employs a single sector provided with an opening larger than the picture plane and rotatable to vary the time required for the opening to traverse the picture plane, thereby determining the shutter speed. According to such system, the sector opening must necessarily be larger than the picture plane in order to provide a bulb (B) shutter or a low-speed shutter.
Therefore, the rotational speed of the sector must be increased to provide a high-speed shutter, but the range of 1/125 to 1/250 sec. would be the maximum shutter speed of such shutter when considered for use in 35 mm still cameras.
A second type is the system disclosed in Japanese Utility Model Publication No. 29806/1969 which, in an effort to eliminate the drawbacks peculiar to the first type, uses a pair of sectors to form an opening which is variable in accordance with the shutter speed setting, the sectors being rotatable while maintaining a predetermined opening during shutter operation.
According to this system, the two sectors must partly overlap each other even for a minimum opening and thus, the composite inertial mass of the two sectors is equal to the inertial mass of a perfect disc having no opening, which is greater than the inertial mass of the single sector of the above-described first type shutter. Accordingly, a greater quantity of energy is required to effect 360.degree. rotation of such two-sector shutter.
A third type is disclosed in British Pat. No. 1,061,605 or Japanese Patent Publication No. 22077/1964, of which the embodiment of FIG. 3 uses two sectors which are individually movable to form a slit with the aid of the time interval between the start of the leading curtain and that of the trailing curtain, as in the usual focal plane shutters. With such system, each sector must be returned to its original position during each shutter charge. More specifically, assuming that the two sectors each make a complete rotation, and if the trailing curtain starts at a point of time very much later than that of the leading curtain as in the slow-shutter or the bulb shutter, the leading curtain which has started earlier opens the shutter and further rotation of this curtain covers the picture plane independently of the trailing curtain. To avoid this, the leading curtain must be stopped at a predetermined angle of rotation, which presupposes the necessity of returning the sectors to their original positions as by winding operation after the completion of the shutter movement, thus sacrificing the ability of the mechanism to accelerate rapidly for continuous shooting as well as complicating the shutter construction.